Sulfur-Deficient Fahlore: Kenoargentotetrahedrite-(Zn) [Ag6]4+(Cu4Zn2)$${\mathbf{S}}{{{\mathbf{b}}}_{{\mathbf{4}}}}{{{\mathbf{S}}}_{{{\mathbf{12}}}}}$$⬜ and Kenoargentotetrahedrite-(Fe) [Ag6]4+(Cu4Fe2)$${\mathbf{S}}{{{\mathbf{b}}}_{{\mathbf{4}}}}{{{\

For the first time in the ores of the epithermal silver-polymetallic Mangazeyskoye deposit (Yakutia, Russia), sulfur-deficient fahlore (kenoargentotetrahedrite-(Zn) and kenoargentotetrahedrite-(Fe)) is found and described using EPMA and single-crystal X-ray diffraction. Keno-fahlore is found as 5‒7 mm crystals on a quartz druse. One of the crystals is a monomineral kenoargentotetrahedrite-(Zn), the other is a polymineral aggregate composed of early argentotetrahedrite-(Fe)-I and kenoargentotetrahedrite-argentotetrahedrite-(Zn) and late kenoargentotetrahedrite-(Fe)-II, pyrargyrite, and miargyrite. The average composition of the kenoargentotetrahedrite-(Zn) (wt %): Ag 32.80, Cu 13.81, Zn 6.84, Fe 0.12, Sb 25.60, As 0.06, and S 20.39, is calculated on the empirical formula (Ag5.79Cu0.21)Σ6(Cu3.93[Zn1.99Fe0.04]Σ2.03)Σ5.96(Sb4.01As0.02)Σ4.03S12S0.12. The composition of kenoargentotetrahedrite-(Fe) (wt %): Ag 25.39–27.90, Cu 17.55–19.76, Zn 0.80–2.67, Fe 3.70–5.60, Sb 26.04–26.65, As 0.07–0.17, and S 21.37–22.12, is calculated on the empirical formula (Ag4.79–4.29Cu1.21–1.71)Σ6(Cu4.02–3.92[Fe1.82–1.23Zn0.23–0.76]Σ1.97–2.05)Σ5.93–6.00(Sb4.04–3.97As0.02–0.04)Σ3.99–4.06S12S0.25–0.55. The refined unit cell parameters of the kenoargentotetrahedrite-(Zn): $$I\bar {4}3m$$ , а0 = 10.483…10.485 Å, V = 1152.17…1152.67 Å3, and Z = 2. The kenoargentotetrahedrite-(Zn) discovered at the Mangazeyskoye deposit is an Ag-, Sb-, and Zn-endmember of the freibergite series, contains larger amounts of Ag and has almost no As and Fe, compared to the prototype of this mineral species from the Yindongpo deposit (Henan Province, China). The Mangazeyskoye deposit is the second locality of kenoargentotetrahedrite-(Zn) in the world and has still been the only one where such an extreme, almost theoretical composition of this mineral is recorded.